Video: Secrets of Swimming in Sand Revealed

Using a lizard, a snaky robot and computer simulations, researchers have captured the secrets of swimming through sand.

Physicists filmed the movements of sandfish lizards and snake-like robots as they burrowed through sand, then boiled their motion down into a numerical theory. The theory ultimately led to a computer model, described in a Feb. 23 study in the Journal of the Royal Society Interface, that can emulate the fluid-like physics of sand and objects that can swim through it.

“They’ve taken advantage of biodiversity to answer questions in physics and inspire new engineering designs,” said biomaterials scientist Kellar Autumn of Lewis & Clark College, who wasn’t involved in the study.

The research, led by physicist Daniel Goldman of Georgia Tech, builds on his team’s previous work. By 2009, Goldman and his colleagues had discovered the sandfish lizard’s sand-swimming motion and designed a snake-like robot to emulate it. In the new study, Goldman’s team used the experiments to create a highly predictive model.

The work may lead to many applications, from landmine detection and earthquake monitoring to sub-surface discoveries on other worlds.

“We’ve never had such a detailed, quantitative, accurate model of an organism moving through an environment that isn’t water or air,” Goldman said. “You can make devices that can sort of wiggle into or through granular materials. We’re already talking to NASA about it.”

Goldman’s team first explored sand-swimming motion by studying sandfish lizards, also known as Scincus scincus. The reptiles are native to North-African deserts and can quickly burrow into sand to escape predators and scorching heat.

The team found sine-wave-like movement allows the lizard, and their robot, to push forward in sand, but creating computer models for the experiments proved problematic. Simulating all of the tiny sand grains required a lot of money to purchase time on powerful computers. So, the team performed the same experiments using 3-millimeter-wide glass beads instead of sand.

“We wanted something easy to simulate that had some predictive power. We got lucky, because it turned out [the lizard and robot] swim beautifully in the same way through larger glass beads,” Goldman said.

When the researchers compared data from all three systems — the lizard, the robot and the simulation — the forces matched within 8 percent of one another.

“That means we can use this model to generate hypotheses, for example, about what is going on internally in the lizard that allows it to swim,” Goldman said. “We can go in and get the physiology of organism and use it to do something useful.”

Only a handful of laboratories research sand-swimming physics, said Stephan Koehler of Worcester Polytechnic Institute, who wasn’t involved in Goldman’s work. Despite the low number, Koehler thinks the implications of such work could lead to world-changing technology.

“As with a lot of basic research, no one sees it seriously until a killer application puts the science on steroids,” Koehler said. “The Wright brother’s work was seen as something of an oddity 108 years ago, and they initially had a difficult time selling their product. But now look where we are.”

Peko Hosoi, a mechanical engineer and roboticist at the Massachusetts Institute of Technology, said work like Goldman’s is crucial for robot innovation.

“You don’t want to blindly copy what animals can do. That doesn’t get you very far,” said Hosoi, who also wasn’t involved in the study. “You need to know the fundamental mechanics behind them to inspire truly useful designs.”

Goldman ultimately hopes to plug models like his team’s into future robots and give them some brains.

“Not just Watson-type machines that can answer Jeopardy questions,” he said. “Ones that can smartly interact with the physical world.”